In prior art motor vehicle designs, engine setting has been achieved by a mechanical linkage between a throttle control element, such as a foot pedal, and a butterfly valve which opens and closes to adjust the amount of combustion air entering the engine intake manifold. With the increasing use of fuel injection, many vehicles employ electronic controls to adjust the amount of fuel reaching the engine combustion chambers. Proposals have been made to directly convert throttle pedal position to an electric signal which controls fuel injection. Such vehicles may not employ any direct mechanical linkage between the throttle pedal and the engine. Instead, the fuel flowing to the engine is controlled by an electric signal whose value varies according to throttle pedal position. In case of a failure in the electronics resulting in false output signals, the vehicle engine speed could become uncontrollable by the operator.
In order to assure safe operation of such vehicles, engine idle validation devices have been employed. When the engine throttle pedal is in its "engine idle" position (e.g. when an operator's foot is off the pedal), an output signal is produced signifying that the pedal is not depressed. When the pedal is depressed beyond a predetermined "idle" position, the validation device signals that the pedal is away from the idle position. Engine operation in response to the pedal position is then enabled.
Idle validation devices have sometimes taken the form of mechanical on-off type switches actuated by the throttle pedal separately from the throttle position signal generator. The mechanical switches had to be installed and calibrated so that they accurately signalled the pedal position. In use, these switches were subject to mechanical forces which shifted them relative to the pedal and to the pedal position signal generator. Besides requiring recalibration, shifting switch settings relative to the pedal position signal generators could disable the vehicle. Moreover, the mechanical switches exhibited fixed relatively wide hysteresis which was undesirable. An example of a prior art proposal of an idle validation device for use with an electronic fuel injection control is disclosed in U.S. Pat. No. 5,133,321 to Hering et al. The Hering et al. patent provided an idle verification device which was fixed in a housing with a pedal position signal generator so that calibration settings could not drift relative to each other. The idle verification switch was provided by a deposited resistance material similar to the deposited material used to form the signal generator. The deposited material forming the idle verification switch was interrupted so that when the pedal was in its idle position one section of the material was engaged by a conductive wiper arm to signal the pedal position at idle. The other section of the material was engaged to signal the pedal position away from idle.
This approach required that the resistance material sections be spaced apart, creating a "dead band" in which the conductive wiper arm engaged neither section of the deposited material. No output of any sort was available from the verification switch in the dead band, which is undesirable. The dead band simulated hysteresis so that the pedal position could be varied somewhat without generating frequent incompatible verification signals.
The present invention provides a new and improved throttle pedal position signalling unit. Wherein independently derived signals both indicate pedal position and validate the pedal position without requiring calibration or periodic adjustments for recalibration.